TRR188 B05 Damage tolerant material design

  Statistical volume element IEHK Statistical volume element for the representative representation of the microstructure of steel

The performance of components is characterized by the microstructure of the material used. To date, there are hardly any quantitative approaches available to reliably describe the influence of microstructural characteristics on the performance of damaged components. Furthermore, only isolated qualitative approaches are available for the design of damage-tolerant microstructures. The targeted setting of a desired component performance capacity, taking into account deformation-related limitations, is hardly possible at present. For this reason, TP B05 pursues the goal of developing quantitative methods for the generic description of damage and microstructure and to use these for a damage-tolerant material design. The subproject thus provides the TRR 188 with an important tool for increasing the performance of components with deformation-related limitations.

The subproject combines process consideration, modeling approaches and experimental characterization methods. It therefore represents a special link between the three project areas of TRR 188.

  Three-dimensional volume model IEHK Three-dimensional representation of a representative volume model

The evaluation of the performance of components manufactured by means of structural engineering is usually carried out based on tests, which are based on the expected component application so that in many cases static and cyclic strength properties as well as residual ductility are evaluated. For this reason, these attempts either lead to a continuation of the ductile damage already initiated during the forming process or to a cyclical damage. The failure behavior on the basis of the first case is, therefore, the ductile damage under non-proportional strain paths. In the second case, however, failure is caused by the superposition of ductile and cyclic damage.

In the first funding period the methodological approaches for the generic description of microstructure and damage are developed. Both the dual phase steel and the case hardening steel are considered. The generation of microstructural models is based on a statistical description of the structure so that artificial microstructures can be generated and evaluated with regard to their performance by setting the appropriate parameters. To this end, the applicant has already developed a methodology that generates generic two-dimensional microstructural models based on statistical structural descriptions. These microstructure models meet the essential requirements of a representative element and also reflect the properties of the present material in a statistically representative way. The construction of the statistically representative artificial microstructure models is extended to three-dimensional elements in the first funding phase due to the voluminous damage characteristics typical of ductile damage (pore development). This pore development is characterized by means of a computer tomograph (micro-CT). In addition, the existing approach for the generation of microstructural models is further developed in such a way that the response of the structures to be imaged includes further parameters. Besides the already considered phase parts, grain size distributions and grain orientations, this also includes particle proportions, particle size distributions, grain orientation distributions, grain misorientation distributions, cell sizes, and pore size and shape distributions. Furthermore, methodological approaches are developed in order to inform (phenomenological) models on superordinate scales.

If the coupling to the macroscopic models is also ensured, this methodology can be used to identify tailor-made materials for defined application areas. Therefore, a computer-based microstructure optimization with regard to the resistance to ductile damage under non-proportional strain paths is carried out in the second conveying period using the example of a dual-phase steel. In the third funding period, the structure of the 16MnCrS5 insert steel is optimized with respect to the resistance to the ductile and cyclic damage. This assignment of the material concepts to the damage mechanisms corresponds to the respective application cases.